Heating filament circuit



AM m, w% E. J. LEUTHOLD 2,346,654

HEATING FILAMENT CIRCUIT Original Filed July 17, 1937 2 Sheets-Sheet 1 INVEN TOR, Edgar J. Leufha/cl.

BY 5 g A TTORNEYS.

Patented Apr. 18, 1944 HEATING FILAMENT CECUIT Edgar J. Leuthold, Newark, N. J., assignor to Tung-Sol Lamp Works, 1110., Newark, N. J., a corporation of Delaware Continuation of application Serial No. 154,419,

July 17, 1937. This application November 24, 1939, Serial No. 306,029

8 Claims.

This application is a continuation of my application Serial No. 154,419, filed July 19, 1937.

This invention relates to heating filament circuits for radio tube sets and a resistance protective unit therefor.

In certain of the conventional radio tube circuits the filaments of the tubes are connected in series with each other and an additional resistance with one or more pilot lights connected across a part of this additional resistance. The filaments are usually of conventional ceramic coated tungsten wire and a high surge current flows through the circuit when the circuit is initially closed, which surge current produces a surge voltage across the pilot lamp or lamps with the result that if the shunt resistance is of a value to supply the required voltage drop to the pilot lamp in the hot condition for efiicient lighting the pilot lamp soon burns out after a few such surges. In practice, however, the shunt resistance is reduced in order to reduce the surge but at the sacrifice of using a lower running voltage across the pilot lamp.

Different means have been proposed in an effort to protect the pilot lamp from the surges and yet have the lamp furnish the desired candle power when the tubes are hot. One such proposal is to introduce into the circuit a high resistance initially and then later a lower resistance in an effort to keep a constant filament current and prevent the overall surge. One objection to this method is that the lowered current in the circuit results in the tubes taking too long to heat up for operation of the set. Another proposed method is the use of a time relay or a heat delay relay which removes a shunt connected across the lamp or shunts out a resistance which is in series with the lamp after a given time delay. Ballast protector resistor units have also been proposed for use in such radio circuits embodying ordinary resistances connected in heat interchange relation or having certain temperature coefficients or both, for the purpose of minimizing the surge across the pilot lamp or lamps. Each of these prior proposed methods is objectionable either because it impedes or delays heating up of the radio tube filaments, or it is complex and expensive, or there is insufficient correlation between the radio tube filaments and the proposed protective means to accomplish perfectly the essentials of quick heating of the radio tube filaments, the prevention of surges through the pilot lamp or lamps, the required light efficiency of the lamp or lamps after the radio set hot condition is reached, and the prevention of burn outs of the shunt resistors when the pilot lamps are out.

One object of the invention is a novel and improved heating filament circuit including a pilot lamp which is characterized by the substantial reduction of or by the absence of the aforesaid objectionable characteristicsfrom the circuit.

A further object of the invention is a circuit of the above indicated character including a resistance unit of novel structure and operation by the employment of which the above indicated essentials of the circuit are accomplished.

The surge in the radio tube circuits including filaments made of ceramic coated tungsten wire is due to or its effect is aggravated by the fact that the additional mass of the refractory or ceramic coating delays the rise in temperature and hence the resistance of the tungsten wire filament which has a positive temperature coefiicient, with the result that there is an appreciable time wherein the resistance in the circuit is comparatively low after the initial closing of the circuit. The ceramic coating seems to form a sort of reservoir for and absorb the heat produced in the filament and to have a cooling efiect, thereby delaying the heating of the filaments.

It is an object of this invention to devise a resistance protector unit embodying a shunt resistor to the pilot lamp or lamps having a layer of refractory material of the same general character of the refractory coating of the filaments of the tubes, and of a depth and mass such that the above indicated essentials of the circuit are obtained and particularly such a protective resistor unit enclosed in an evacuated bulb.

Other objects of the invention will hereinafter appear.

For a better understanding of the invention reference may be had to the accompanying drawings, wherein- Fig. l is a diagrammatic view illustrating the circuit in theapplicants protector unit;

Fig. 2 is a side view of an element of the unit with parts broken away;

Fig. 3 is a perspective view of the elements of the unit in assembled position;

Fig. 4 is a cross section of the wire of the shunt resistor element;

Figs. 5 to 7 illustrate a modified form of construction embodying the invention;

Fig. 8 shows a modified detail;

Figs. 9 and 9a show another modified form of device embodying the invention; and

Figs. 10, 10a and 11 illustrate further modifications.

Referring to Fig. l of the drawings, the numeral I indicates the several radio tubes of a radio tube set having heating filaments 2 therein which are connected in series with a pilot lamp or lamps 3, only one such lamp 3 being illustrated in the embodiment shown. The heating filaments 2 are or may be of conventional tungsten wire coated with a ceramic or other refractory material, such for example as aluminum oxide, magnesium oxide, beryllium. oxide, titanium oxide, zirconium oxide, or any combination of these oxides with silica which will form a eutectic and the melting point should not be less than 1400 C., or silica may be used alone. Filaments with thin coatings of ceramic material are used in many of the radio tubes. The circuit is connected across either an A. C. or D. C. supply line indicated at 4. The novel protector unit is indicated at 5 and comprises a shunt resistor filament 6 contained in an evacuated envelope 5 and connected in shunt to the pilot lamp 3. The resistor 6 is formed of tungsten wire l with a mass of a refractory material 8 thereabout. The body- 8 may be of the same refractory material utilized in coating the filaments 2 of the radio tubes.

The resistor 6 maybe formed and coiled to assume any suitable form, but. the formation of the same into a multiplicity of loops, illustrated in Figs. 1 and 2, to obtain the required length of resistor and the disposition of these loops within a flat tube or envelope It, as illustrated in the drawings, results in a convenient and satisfactory unit. A flattened tube ID of metal, as of nickel or nickel alloy, is preferable. The envelope I0 may be mounted in any suitable manner upon the press II, and in the particular embodiment shown a support wire I2 is fused into the press adjacent one edge thereof with a bend l'3formed' therein intermediate the ends of the support wire, andthe upper end l4 being disposed parallel to the lower part thereof to which part M the envelope lfi' is'directly fastened. This fastening is effected by metallicbands I'5- passing around the wire M and the envelope [0 and welded thereto, the wire part I4 engaging the edge of the envelope. Another anchoring support for-the envelope is indicated at Hi, this support being fused into the press H and being welded at I! to the side of the envelope at the lower end therecfv Current is connected to the resistor unit 6 by means of the conductors l8 fused into the press.

In the particular embodiment shown the evacuated tube 5 also contains a line resistor unit 20. This embodies a mica strip 2| having wound therearound the required resistance wire 22. This line resistor may be mounted in any suitable manner upon the press H and in the particular embodimentv shown it is mounted upon a pair of support wire 24 and. 25 which are fused into the press. At the upper end of the support 2-5 a portion 24' is carriedat right. angles to the upright part 24 and the free end of the part 24 is welded or otherwise fastened to a metallic bead or eyelet 26 mounted in the mica. The support 25 is bent over to form a downwardly extending part 21 which is again bent at right angles to form a part 28 and the free end of the latter is turned upwardly and welded or otherwise fastened to the eyelet or head 26 fastened near the lower end of the mica strip 2|. The support wires 24 and 25 also form the current leads for the unit, the ends of the resistance wire 22 being electrically connected with the beads or eyelets 26. Thus, in the particular embodiment shown, the line resistor unit 20 is disposed adjacent to but spaced from the envelope Ii).

The refractory body 8 for the tungsten wire I may be. of any suitable depth to produce the desired. results. I have found, however, that with the tungsten wire I of approximately a diameter of .00138 to .0017 inch and applying a refractory or ceramic layer to a, depth of approximately .0045 to .005 inch, making a total over-all diameter of approximately .011 to .012 inch, and making the resistor of the required length when hot to give the required voltage drop across the pilot lamp 3 for emcient lighting and: long life and enclosing the. resistor unit in the evacuated bulb 5, effective protection of the pilot lamp 3 is obtained against surges while the rate of heating of the filaments 2 is not decreased.

A suificient length of the wire 1-8 may be readily assembled into the fiat tube or elongatedenvelope ill, the loops of the resistor being contained within the plane of the envelope. The depth of the body 3 of the wire, may as indicated, be varied within limits. If the depth or thickness is no greater than the thickness of the refractory coating on the filaments 2 the resistor would not remain cool long enough on the surge to produce the best results, but by making the depth of the body 8 of the resistor greater, as for example approximately twice to four times the depth of the coating on the filaments 2, the desired delayed heating of the wire 'I and elevation of the resistance is obtained at the start. This greater depth of coating makes it possible for the shunt resistor-,particularly when contained in the evacuated bulb, to withstand the full set current when thepilot' lamp either burns out or is removed. The mass on the wire seems to absorb the heat as it builds up from they wire and prevents the resistance of the wire from building up too rapidly. At the initial resistance of the resistor the surges of current through the ceramic coated filaments do not produce a harmful drop across the pilot lamp. Generally; the greater the initial cooling the less the final resistance needbe and hence the less final heating of the ceramic filament, and hence the tungsten wire 1 need not be placed close together but can be spread outin co-planar relation within the envelope 10.

By using the construction described above it has been found that the. resistor will withstand not only the normal surge of. current while in parallel with the pilot lamp, but will withstandfull set current surge with the pilot lamp out and continuous full set currentwhenthe set is operating without pilot, and there is no appre ciable slowing up of the heating of thefila-ments 2 of the tubes. The resistor 1-8 ordinarily glows. brightly when the pilot lamp is out and the set current is reduced slightly but the-reduction,-

is not enough to interfere with the operation of the set.

.The resistance wire 1 should have a high positive temperature co-efiicient of resistance and a high melting point such as tungsten. It must be fine or small enough so that it can build up'its temperature at the running by-pass current (as for example .150 ampere through resistor, .150 ampere through 6.3 volt pilot lamp, set current .300 ampere). The flattened nickel tube l helps the resistance wire to conserve its heat for the building up of its resistance, while the ceramic or refractory body 8 delays the heating of the wire for an appreciable period after the initial closing of the circuit. By positioning the resistor in an evacuated bulb it may be heated to the glowing temperature without burning out and there is no gas present in the evacuated bulb which would tend to keep the resistor I too cool and would limit its heat build up. The vacuum also assists in preventing heat exchange.

The resistance wire 22 may be of any suitable character such asNichrome wire .004 inch in diameter and this wire is preferably coated with the ceramic or refractory material, as for example the above described material, and while the resistor unit may be mounted outside of the bulb 5' it is preferably mounted therein and in the particular embodiment shown there is no appreciable heat interchange between the elements 6 and 20.

In the modification of Figs. 5, 6 and 7 the shunt protector resistance unit is indicated at 30, while the series resistor is indicated at iii.

The unit comprises a bunch of loops of resistance wire 1-0 of the character shown in Figs. 1 to 4 mounted within the metallic envelope or tube 32 and this tube 32 may be supported in any suitable manner upon the press H, as for example by means of a wire support 33 to which are welded a pair of fittings 34 carrying the tube 32. The terminals 35 of the resist ance units ii-13 are electrically connected with the wire support 33 and a wire terminal 36.

The series resistor unit 3! comprises a refractory tube 00 inserted over a support wire 4!, with the series resistance wire 22 wound or coiled about the tube 50, one end of the resistance wire 22 being electrically connected at 42 with the upper end of the support wire M, and the other end being electrically connected with the terminal 35. The assembly of the tube 40, the wire support it and the resistance wire 22 is preferably dipped in a suitable refractory material, such for example as of aluminum magnesium silicate to form an insulating coating 43 about the tube 50. This coating 3 assists in anchoring the parts together. The tube 50 may be of any refractory material.

In the modification of Fig. 8 a metallic tube 32' for housing the shunt protector resistance 1-8 is formed from a metallic sheet as of nickel, with two mating parts 05 forming the means for mounting of the unit upon the wire support 33 as by welding.

In the modification of Figs. 9 and 9a an elongated refractory block 4t is provided for housing both the shunt protector unit and carrying the series resistor unit. This block 05 is provided with a small opening 41 lengthwise thereof for the reception of a support wire 48. The series resistance wire 22 is wound about the exterior surface of this block 46 and one end of this resistance wire is electrically connected to the upper end of the wire support 48 and the other end is electrically connected with a wire terminal 49. The. block 46 is provided with a reception of the larger opening 50 lengthwise thereof for the shunt protector resistance 1-8 and the terminals of the resistance protector 18 are electrically connected respectively with the wire support 48 and a wire terminal 5|. The block it may be dipped to form a coating 52 thereabout similar to the coating 43 of Fig. '7.

Figs. 1.0 and 10a show a modification similar to Figs. 9 and 9a except that here the block 46 is provided with a pair of openings 50 lengthwise thereof to house a pair of protector resistance units 7-8 for a pair of pilot lamps.

The modification of Fig. 11 is similar to the modification of Figs. 5 to 7 except that here the metallic tube 32 is duplicated for the housing of a pair of shunt protector units 1-8 for protecting a pair of pilot lamps. These two tubes 32 may be fastened to the wire support 33 by means of fittings 34'.

The circuit of Figs. 5 to 9is the same as that illustrated in Fig. 1, and the circuit of Figs. 10 and 11 differs from the circuit of Fig. 1 only in the provision of a pair of pilot lamps 3 instead of one, in shunt to each of which is connected a shunt protector unit 1 8.

The operation of the modified device of Figs. 5 to 8 and Fig. 11 in the circuit is the same as described above with respect to Figs. 1 to 4, except that here the series resistor 3| is still further removed and spaced from the shunt protector unit with a minimum heat interchange between the two units. In the operation of the circuit including the modified device of Figs. 9 and 10 the heating up of the shunt resistance l-8 after closing the circuit is hastened because of the heat interchange relation existing between the series resistance 22 and the shunt protector resistance 7-8. Otherwise, the operation is similar to that described above. The bunching of the loops of the filament i8 contained in the enclosure result in some heat interchange between the loops.

The ratio of the overall diameter of the protective resistor wire to the tungsten wire diameter forming the core of the wire ranges from 5.8 to 8.5. The ratio of overall diameter to the tungsten wire diameter on certain commercial radio tubes having filament wire diameters of from .0014 inch to .0118 inch ranges from 4.67 to 5.6, the 4.67 ratio, for example, applying to the .3 ampere tubes used in the series circuits of modern receivers and the 5.6 ratio applying to the .15 ampere tubes which are used chiefly in auto mobile radio sets. With the use of .15 ampere pilot lamps (designated 3 in Fig. 1) in the circuits of modern sets wherein the voltage across the circuit is volts and the current of the heating circuit .3 ampere, I have found protective resistor units embodying the invention of this application as particularly suitable having the following specifications:

I claim:

1. A resistance unit for protecting a pilot lamp connected in circuit in series with radio tube heating filaments, comprising a resistance wire element enclosed in an evacuated bulb. and adapted to be connected in circuit in parallel with said pilot lamp, said wire having a positive temperature coefiicient and having therearound a refractory electrical insulating body of relatively large volume in thermal relation therewith the ratio of the thickness of the insulating body to the diameter of said wire being greater than the ratio of the thickness of the coating on each heating filament to the diameter of such filament and so related thereto as to first delay the heating of the resistance wire up to its normal operating temperature at the initial closing of the circuit and then to permit a rise to the normal operating temperature and resistance thereof.

2. In a heating filament circuit for radio tube sets, a plurality of radio tube heating filaments, said filaments having a refractory coating thereon with the ratio of the overall diameter of the coated filaments to the filament wire diameter from 4.5 to 5.6, a pilot lamp connected in series with the aforesaid filaments, a protective resister connected in parallel with said pilot lamp, said resistor being mounted within an evacuated bulb and formed of wire having a positive 'temperature coefficient and provided with a refractory coating thereon with the ratio of the overall diameter of the protective resistance wire to the wire diameter forming a core from 5.8 to 8.5.

3. In a heating filament circuit for radio tube sets, a plurality of radio tube heating filaments, said filaments having a refractory coating thereon with the ratio of the overall diameter of the coated filaments to the filament wire diameter approximately 4.6, a pilot lamp connected in series with the aforesaid filaments, a protective resistor connected in parallel with said .pilot lamp, said resistor being mounted within an evacuated bulb and formed of wire having a positive temperature coeflicient and provided with a refractory coating thereon with the ratio of the overall diameter of the protective resistance wire to the wire diameter forming a core from 5.8 to 8.5.

4. In a heating filament circuit .for radio tube sets, a plurality of radio tube heating filaments, said filaments having a refractory coating :thereon with the ratio of the overall diameter of the coated filaments to the filament wire diameter approximately 5.6, a pilot lamp connected in series with the aforesaid filaments, a protective resistor connected in parallel with said :pilot lamp, said resistor being moun ed within :an evacuated bulb and formed of wire :having apositive temperature coefficient and provided with a refractory coating thereon with theratio of the overall diameter of the protective resistance wire to the wire diameter forming a core from 5.8 to 8.5.

5. In a heating filament circuit for radio tube sets, a plurality of radio tube heating filaments,. said filaments having a refractory coating thereon, a pilot lamp connected in series with the aforesaid filaments, and a protective resistor connected in parallel with said pilot lamp, said resistor being mounted within an evacuated bulb and formed of wire having a positive ternperature coefficient and provided with a refractory coating thereon, the ratio of the overall diameter of the protector resistance wire to the wire diameter being greater than the ratio of the overall diameter of the coated heating filaments to the diameter of the heating filaments and so related thereto as to effect a delay of the heating of the protective resistance wire up to its normal operating temperature and resistance at the initial closing of the circuit while permitting a subsequent rise to such normal operating temperature and resistance.

6. In a radio set having vacuum tubes with resistance elements therein certain of said resistance elements serving as heaters for cathodes, a circuit in which said resistance elements are connected in series across a source of power, a dial light connected across a portion only of one of said elements, the said portion of said last named element having a longer thermal lag than the element of the remainder of said tubes in said radio set.

7. In a heating filament circuit for radio tube sets, a plurality of radio tube heating filaments, said filaments having a refractory coating there on, a pilot lamp connected in series with the aforesaid filaments and a protective resistoir filament connected in parallel with said pilot lamp, said filaments thus forming a series circuit with the combined currents which flow through the parallel lamp and protective resistorfilament circuit flowing through the other filaments, said resistor filament being also mounted within an evacuated bulb and formed of Wire having a refractory coating thereon, the protective resistor filament having a positive temperature coeificient of resistance and an inherent time element lag with respect to the heating up of the others of said filaments so as to effect a delay of the heating of the protective resistor filament wire up to its normal operating temperature and resistance at the initial closing of the circuit while permitting a subsequent rise to such normal operating temperature and resistance.

8. In a heating filament circuit for radio tube sets, a plurality of radio tube heating filaments connected in series, a pilot lamp and a protective resistor filament connected in parallel and in series with the aforesaid filaments, said filaments forming a series circuit with the combined currents which fiow through the parallel lamp and protective resistor filament circuit flowing through the other filaments, said protective resistor filament being also mounted within an evacuated bulb and being confined in loops in an envelope, the protective resistance filament having a positive temperature coefiicient of resistance and an inherent time element lag with respect to the heating up of the other filaments in the circuit so as to effect a delay of the heating of the protective resistance wire up to its normal operating temperature and resistance at the initial closing of the circuit while permitting a subsequent rise to such normal operating temperature and resistance, and the constants of the filaments and the lamp being such that the operation of the set is unimpaired upon the disconnection of the pilot lamp.

EDGAR J. LEUTHOLD.

CERTIFICATE OF CORRECTION. Patent No. 2,5L 6,65L April 1 19m,

EDGAR J. LEUTHOLD.

It is hereby certiflied that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1;, first column, line i claim 1, before "heating" insert -coated--; and that the said Letters Patent should be read with this correction therein th t th same may conform to the record of the case in the Patent Office.

Signed and sealed this 5Oth day of May, A. D, 19%.-

Leslie Frazer (Seal) Acting Commissioner of Patents. 

